Typical suspension designs for snowmobiles have relatively high unsprung weight values for the components due to the fact that most, if not all, components are arranged within the confines of the track perimeter and move when the suspension deflects vertically. In current snowmobile designs, as much as seventy percent of the weight of the snowmobile is unsprung weight. In addition, prior art systems have what is referred to as falling rate or constant rate spring force/vertical travel characteristics. This produces unfavorable rider comfort levels when attempting to tune a suspension system with a single combination of spring and damping rates to be comfortable when traveling over low or smaller bumps, while being able to absorb high or deep level terrain.
There are three typical rear suspension adjustments in most snowmobiles today which consist of spring rates, a coupling between front and rear arms, and a front skid rail limiter strap to control weight transfer. All three of these adjustments are accomplished by means of mechanical adjustments made with various tools, and the actual locations for each are within the general confines of the track in areas that are prone to snow and ice accumulation and freezing of the various components required to make the adjustments. Due to the difficulty involved in making adjustments, and the operator's ability to quantify or realize the improvement (or lack thereof) because the snowmobile must be stopped in order to perform the tasks, this often results in the situation where the rider is either too inconvenienced to make changes, or doesn't readily feel the differences when adjustments are made.
U.S. Pat. No. 6,032,752 is an invention for a semi-active rider controlled rear shock angle device. There are also several types of rider-controlled shock valve damping devices in snowmobiles. The first mentioned device does not offer any improvement to reducing unsprung mass and is very prone to failure due to freezing of mechanical components. Tuning of shock valving has limited affect on overall suspension characteristics. None of the existing designs provide a driver controlled method for changing the front skid frame limiter strap adjustment or an adjustment for rider controlled coupling changes between the front and rear arms of the rear suspension system. A change in the coupling of the arms has a significant impact on weight transfer, cornering ability, and rider comfort. All three of the typical adjustments of a rear suspension system must work together to realize the most gain from each individual adjustment. Existing designs only offer limited ability to change the overall adjustment capability and overall performance resulting from these changes.
Thus, there is a general lack of comfort in riding due to lack of ideal suspension tuning for changes in rider(s) weight, and most of all, varying trail and terrain conditions such as types of bumps, riding speeds, and types of corners encountered in everyday riding conditions.